only listen to stream errors if not already

lib/application.js

@@ -195,7 +195,7 @@ function respond(next){
 
     // Stream body
     if (body instanceof Stream) {
-      body.on('error', this.onerror.bind(this));
+      if (!~body.listeners('error').indexOf(this.onerror)) body.on('error', this.onerror);
       if (head) return res.end();
       return body.pipe(res);
     }